Toyota Coaster Bus Conversion – Plumbing Guide

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There are many ways to design a caravan or RV plumbing system for your bus conversion.

It can range from something simple with a manual pump connected to a jerry can to an advanced system like what we have in our Toyota Coaster.

A system like the above is about as basic as it gets. It uses two portable water tanks (jerry cans), one for fresh and one for grey water. Upgrading the manual pump to a 12v/24v pump would improve the use of the system while still keeping it fairly simple.

This is a diagram of the plumbing in our Toyota Coaster bus

Starting from left to right, following the flow of water:

1 – Lockable Water Filler with 25mm Outlet

So that each water tank can be filled individually, two lockable water fillers are installed on the external of the bus. They connect to the water tank with a 25mm food grade hose, and a 10mm hose. The 10mm hose acts as a breather and helps the air release when the tank is being filled with water. This improves the speed in which the tank fills. Once water comes up this breather and back out the inlet, you know the water tank is full.

2 – Custom Coaster Conversion Water Tank (Fresh Water)

We installed two Custom Coaster Conversion water tanks underneath the bus behind the rear tyres. They carry approximately 70l of water each and are made from a food grade poly.

140L of water allows us to go around 4 days between filling up tanks.

Our tanks are setup to be filled separately by two water fillers and accessed individually by two pope in-line taps.

If you did want the water to pull from two or more tanks at the same time, you must ensure they are installed an equal distance from the pump. If they are not at equal distances, the pump will empty the closer one first, and then struggle to empty the second as it will continue to try and pull from the first. Alternatively some tanks can be installed as a primary and secondary, allowing the need for only one fill point.  

3 – Pope In-Line taps

The Pope In-Line taps allow each of our tanks to be isolated and used individually. When one tank is empty we switch over to the other tank manually and the pump pulls the water from the next one. Make sure these taps are installed in a location that is easily accessible as they will need to be changed regularly.

4 – Shurflo 4009 pump and filter

The water tanks are connected to the inlet of the Shurflo 4009 pump with 13mm drinking hose. From the outlet of the pump to all appliances, 12mm John Guest pipe and fittings are used. When using semi-rigid hosing, SHURflo recommends using 300mm of flexible hosing either side of the inlet and outlet to prevent vibration of the hoses (we have not used this and have not found it to be a problem).

The SHURflo pump requires a filter to be used for warranty. The pump does not require an accumulator to be used, which means it provides a consistent flow on its own and maintains a constant water pressure. If for some reason, you are finding that you are not able to maintain pressure you can still add one to help improve the water flow.  

5 – John Guest One-Way Non-Return Valve

A non return valve is required when adding a mains water inlet. The one closest to the pump prevents mains water from entering back into the pump, and the one closest to the mains inlet prevents water from exiting back out the inlet. 

In other words, the non-return valves keeps the water flowing one way, in the direction it is supposed to.

6 – SHURflo Mains Pressure Regulator Water Inlet

A water inlet allows you to connect your bus conversion up to a mains water supply to use instead of your water tanks (for example, when parked at a caravan park). Our hot water system requires a pressure of no more than 50psi, so we installed a ‘Shurflo pressure regulating water inlet’ to regulate the pressure.

If you are using a standard inlet, a separate pressure regulator may need to be fitted. Make sure to check the specifications of your appliances to ensure any limitations are met.

To attach a regular garden hose/drinking water hose, from a mains supply to the inlet, a brass click-on to 3/4 NPT fitting is used. 

7 – Appliances (Suburban SW6DEA HWS, Dometic CTS 4110 Toilet, Camec 3KG Top Load Washing Machine, Kitchen Sink, and Shower)

12mm John Guest semi-rigid pipe is a flexible but firm water pipe that is perfect for use in a motorhome or bus conversion. It is used for to connect each appliance or tap in your plumbing system back to your water pump. The pipe runs underneath the bus, and in the walls and cabinets of our Toyota Coaster bus to our appliances.

Look at the instructions for each appliance you have and get a fitting that connects the john guest pipe to the required size (we will talk about the connections for each of our specific appliances below). 

8 – Custom Coaster Conversion Water Tank (Grey Water)

A grey water tank is used for all of the ‘dirty’ water to go. For example, water used during a shower, or the kitchen sink. The shower and sink are connected to the grey water tank with a 25mm hose. A sink trap is used on the kitchen sink to prevent smell from returning back from the tank. It is an ‘S’ shaped pipe which traps the smell in the bends and stops it coming back into the bus.

In the shower, non-return valves are used to prevent the grey water coming back up the drains and into the shower. This can happen when the shower outlet and tank inlet are at approximately the same height.  

Detailed Steps To Install Each Item For Your RV Plumbing – 

Please note – These steps assume you have installed your tanks under the bus, see our post here on how to do this.

Toyota Coaster Motorhome Conversion – RV Fresh and Grey Water Tank Install

To avoid repeating over and over, assume all barb fittings have an appropriate sized hose clamp. All John Guest connections use the optional locking clip.

See the videos throughout the post on how to do most of these steps. These may be easier to follow.

Lockable Water Filler –  

• First step is to locate where you would like to install the fillers for your fresh water tanks. As our fresh tanks are at the rear of our bus (behind the rear wheels), we chose to install them at the back, and around halfway up the side of the bus (above the floor line).  Using a metal hole saw piece for your drill, cut a 88mm sized hole where you have chosen. Make sure your hole-saw piece is just slightly bigger than your water filler so that it will sit in flush.  
• (Ignore this step if your tanks are not installed under the bus floor). Start by drilling two holes in the internal floor of your bus near where you have just cut the hole in the wall (approximately 29mm and 13mm) this will be where you run your two hoses that go from the filler to the tank.  

• After you have cut your holes, feed the 25mm and 10mm hoses through the water filler hole, and then through your holes in the floor and down to your tank. You can now attach the hoses to the barb fittings on your tank. 
• Now it is time to cut the hose where it is coming out of your filler hole. Make sure that it is not pulling too tight as you don’t want it to cause kinks. Attach the hoses to the barbed end of the water filler. 
• Test putting water in the filler, to ensure there are no leaks, prior to attaching the filler to the bus wall to make it easier to correct any issues. Make sure the filler is orientated so that the breather is at the top.
• The last step is to silicone the rim of the filler and place it in the hole you have cut on the bus. Drill 4 pilot holes in each corner marked on the filler, and then use stainless steel screws to fix to the bus (alternatively, we used pop rivets). 

Water Tanks and In-line taps – 

• Find a spot where you will install your in-line taps and combine both tanks into the one feed. Make sure these taps are installed in a location that is easily accessible as they will need to be changed regularly.
• To do this, combine a 25mm/20mm all female BSP ‘T’ connector with 2 male/male connectors. After this, connect 2 female/female elbow connectors. Then connect a 25mm BSP to 13mm Barb to all 3 ends. See picture below for a clearer idea as it sounds confusing! Mount this to the wall or floor where you have chosen. We mounted ours under our bed, above our water pump.

• Now it’s time to drill two ~15mm holes in the floor near where you will have your in-line taps, this is where you will run your hoses from the tanks. 
• One side at a time, feed the hose through the hole and route to your tank. Connect to the 13mm barb on your tank. 
• Cut the other end of the hose where you have chosen to have your in-line taps. After you have cut it, connect the end to one side of the in-line tap and run another small piece of hose from the other end of the tap to one side of your 3 end join. 
• Repeat for the other tank. 

SHURflo 4009 and Filter – 

• Start by connecting the filter to the inlet side of your pump (only hand tighten). 
• Then attach the 13mm hose to the middle part of your 3 ended joiner. 
• Next, cut this hose near the filter and attach to the barbed end of the filter. 
• Finally, attach 1/2 BSP to 12mm John Guest and connect to the outlet side of your water pump.

Mains Inlet and Non-return valves –

• Install the mains inlet the same way as the water fillers above, using a 88mm metal hole saw in the desired location. We installed ours next to one of the water fillers and near where our water pump was located.
• Attach a 1/2 inch BSP to 12mm john guest fitting to the outlet of the mains inlet.
• Run a small piece of 12mm john guest pipe, then connect this to a john guest non-return valve
• Run another small piece of 12mm john guest pipe to a T connector
• Connect another end of the T connector to a non-return valve that then connects back to your water pump

You can now run blue John Guest hose from your water pump to all of your appliances, using ‘T’, Elbow and Y connectors. I will assume all hose has been run for the remainder of the appliances and just talk about the connections.

All John Guest hot water hose connections need the optional plug inserted. 

Suburban SW6DEA Hot Water System – 

• Start by connecting the brass 1/2inch to 12mm John Guest fittings (we used elbow connectors) to the cold water inlet and hot water outlet on the back of your hot water system. It is important you use brass, as it is required to comply to watermark certification. 

• Then connect the cold water and hot water hoses to the connectors, as marked on your system.
• From here run hot water hose to required appliances using ‘T’, Elbow and ‘Y’ connectors like the cold water hoses. 

Dometic CTS 4110 Toilet –

The Dometic CTS 4110 toilet requires a 1/2inch NPT connector which is unavailable in Australia. After much research it seemed that 1/2inch was the only size fitting that could be interchanged between BSP and NPT. So we had to connect the 1/2inch BSP/NPT to 12mm John Guest fitting and then connect the hose. We found ours dripped very slightly (we blame the BSP) so to try to alleviate this problem, we wrapped it in silicone tape to form a seal.  

Camec 3KG Top Load Washing Machine – 

1. When we asked a caravan parts store for a BSP to John Guest fitting of the right size, we were told that all Caravans, (and therefore we should) install the washing machines with a standard brass tap, similar to a house. It is a good idea as it allows you to turn the water on and off to the washing machine separately. Mount your tap with screws to the desired place on your wall.
2. Then, attach the 1/2inch BSP to John Guest fitting to the inlet of the tap. 
3. Finally, attach the standard washing machine hose to the outlet of the tap and turn tap on (We do not recommend turning it on all the way, we haven’t found an exact amount/pressure but just turned it on a rotation or so. We found too much water pressure causes there to be a leak at the connection points).

Kitchen Sink/Faucet – 

• Start by attaching a 1/2inch BSP to John Guest fitting to the cold and hot water inlet (on the end of the flexible metal hose of the tap).  

Our sink, being a standard kitchen sink, came with a 50mm outlet. A caravan specific sink will come with a 25mm outlet which can be run straight to your greywater.

If you would like to connect a S trap for your RV plumbing like we have, you can purchase a 25mm to 50mm step up then follow our instructions below.

• Then attach the S trap to the 50mm waste of the sink.
• Next, install the 50mm to 25mm adaptor to the bottom of the S trap. It may be a better idea to step down in smaller increments if your supplier has a way of doing that. We are concerned of waste build up on the shelf of this adaptor, however did not have an alternate option at the time.
• Finally, connect the 25mm waste hose and run it to the grey water.  

Shower –

• Start by connecting a Sharkbite Copper Lugged Elbow 1/2inch to Sharkbite Copper Straight Connector 1/2inch  with copper pipe.
• After this, drill a 13mm hole in your shower wall where you want your shower head connection to be and insert the copper lugged elbow into this hole. 
• Then, attach a 1/2inch BSP to John Guest fitting to the end of your Sharkbite Copper Straight Connector. 

Our shower has a single tap that controls hot and cold. The next few steps of instructions may vary slightly if your hot/cold tap are separate.  

• Start by using a jigsaw or drill to make a hole large enough to install your tapware. For us we traced around the hole for the plate that fit around ours, and cut a hole with the jigsaw. Install the connection for your tapware into the hole. 
• Attach 1/2inch BSP to John guest fittings to all 3 BSP ends of the ‘T’ piece that came with your shower tap. Connect your hot water and cold water John Guest hoses to the ends of the ‘T’. 
• Next, connect a John Guest hose from the top of the ‘T’ connector to the bottom of the Sharkbite Copper Straight Connector. 
• Attach your showerhead and tapware to the fittings.

Shower Grey Water –

• The custom coaster shower base is designed to fit the ‘SMEV straight waste’ outlet. Silicone the rim of your ‘SMEV straight waste’ and install this into the pre-cut holes in the shower base.  
• Next, attach a 25mm hose to the waste outlet.  
• Finally, join the waste hoses together with ‘T’ Connectors. Once all the hoses are converging to a single point, install a 25mm non-return valve.

Grey Water Tank –  

• Start by connecting the 25mm hose from the sink waste and shower waste non-return valve with a ‘T’ connector. Run a hose from the ‘T’ connector to the 25mm to 3/4inch BSP installed into your grey water tank.
• Next, connect a 10mm hose to the barb fitting on the tank to act as a breather. This will assist with draining your sink and shower grey water. Drill a hole in your floor and run the hose up along your shower wall, that is higher than waste outlets.

If you want to be safe from leaks you can drill a hole into your shower and feed the hose into this. That way if the grey water fills and starts coming up your breather, it will drain into your shower. 

Conclusion

Plumbing for your bus conversion can be tricky! There are a lot of variables and each situation is unique. We have tried to be as thorough as possible, and have included links to our videos, and items so that you can view to hopefully make things easier. If you would like more information or something is confusing, please send it through to us via the ‘Contact Us’ section and we will try to help ?