If you’re building a camper or RV you may be interested in adding a Grey Water Holding Tank. With so many National Parks and other budget campsites requiring campers to be self contained it’s not a bad idea. It is nice to be able to pull up wherever you like and have a meal or even a shower without leaving a mess on the road. You could install your own tank for about $150-$250 including brackets, bolts and plumbing parts, however the first challenge is to figure out if you have room for a tank or not. If you will only be installing a kitchen sink you could place a gray water tank inside the living space like under a bed or in a cupboard, but you need to set it up so that you can empty it easily. You also have to consider how you will vent the tank if it’s inside the camper. The tank vent should discharge to the exterior of the vehicle so that you don’t have dangerous gases and odors inside the camper. If your going to install a shower then you will likely have to fit the grey water tank under the floor of the camper, this is probably the best place for a grey water tank as it free’s up valuable storage space inside the camper, gets the center of gravity down a little lower, it can be vented to the exterior easily and is easier to empty.
I recently added a grey water tank to my Ford Transit Camper Van, as it has a kitchen sink, a vanity sink and a shower tray to drain. I needed to mount the tank under the floor of the van, however space is limited. The van already had an 83 litre fresh water tank mounted under the chassis along with a large fuel tank, a spare tire and the exhaust system, this doesn’t leave too many spots for another tank . However I found a spot between the spare tire and differential and took a rough measurement of the area I had to work with, then searched the internet for an appropriately sized tank. Most fresh water tanks aren’t suitable to use as grey water tanks as their inlets and outlets are too small, usually their outlets are only 1/2”. The minimum inlet and outlet size on a grey water tank should be 1-1/2” or 40 mm with many holding tanks having 3” outlets.
I found a 50 L tank on ebay for $75.00 and it has two 1-1/2” threaded outlets with BSP threads – one at the top and one at the bottom. At the hardware store I bought a couple of male 1-1/2” threaded PVC fittings that screw straight into the tank that will accept 1-1/2” PVC pipe, I wrapped thread tape around the threads before installing to ensure a good fit. The tank I bought is made of polypropylene and most sealers won’t stick to it, so thread tape works the best at sealing the threads. I bought some galvanized steel strips to make the tank holding brackets, then I cut them to length and bent them to shape and drilled holes in each end. I found some existing holes in the chassis rail so I did’t have to drill any holes in the chassis, then I just bolted the steel to the chassis, formed the steel around the tank and then bolted the two ends of the galvanized steel strips together. If using a thin walled tank it’s a good idea to mount a thin steel plate under the tank to shield it from flying stones, I didn’t do this and so far I’ve had no damage to the tank. You can purchase more expensive tanks with thicker walls that don’t need shielding.
I wanted to add a vapour or P Trap to stop odors from the tank entering the living space, but I have 3 drains and the shower drain is directly above the spare tire so there is no room for a trap under the shower stall. I also have a drawer directly under the kitchen sink so not a lot of room under the sink, so I decided to add a trap to the inlet of the grey water tank. This frees up space under my sinks and I only need to install one trap to service all three drains, I think it only cost me $10 for the trap. I had to adapt down to 1-1/4” to attach the P Trap to the tank and when gluing PVC pipes together you need to use PVC primer before adding the glue or the pipe joints will leak. This plumbing system could also be constructed with ABS drain pipes and ABS cement, I used PVC because that’s what is available at my local hardware store.
From the bottom outlet of the tank I immediately added a 90 degree angle to the PVC pipe and directed the out feed pipe towards the rear of the van. Under the rear bumper I added a PVC ball valve tap to allow me to empty the tank, to install this I made a small steel bracket to support the end of the pipe. I bought a roll of drain hose and it fits perfectly into the end of the ball valve which allows for running the grey water to the sewer dump points at campgrounds.
The drain holes I bought with my sinks and shower have 1” barbs on the bottom of them so I simply attached 1” drain hose to each sink and joined them into a plastic irrigation T fitting then ran a single 1” drain hose through a hole drilled through the floor towards the Grey Water Tank.
I joined the 1” drain hose from the 3 sinks with the 1” drain hose from the shower with another T piece then ran the T fitting into the trap using thread tape. The tank I bought didn’t come with a vent so I had to drill a small hole in the top of the tank then add a length of 3/8” clear vinyl tubing to allow air out of the tank while water is entering. If the tank doesn’t have a vent, water can’t pass through the P Trap, I know this because I tried running water down the sink and it didn’t work then I drilled the hole. Now this system works well, water flows down the drains smoothly and there are never any bad odors in the van!