Teardrops n Tiny Travel Trailers

Hey all. It's a long story but I'm redoing a mixed black/grey (solo) holding tank on our latest mini-trailer and making it strictly grey and then adding a cartridge toilet instead which is a far more convenient setup. The existing tank was leaky, the single mixed tank wasn't ideal, and when I dropped it, it didn't take me long to figure out why it was leaky - the installation (either factory, or some previous owners modification) was a total gong show with caulking trying to make up for it. I think Ray Charles cut the hole, suffice to say.

Anyhow, I have the tank at a reputable plastic welding shop getting returned to basically new (and hole-less) condition. It's in otherwise good condition and was a waste to throw away when I could get it fully repaired for 1/3 the cost of a new replacement.

For the revised setup I need 3 (probably 1" will be fine) holes on the top of the tank near where the toilet used to drain into. 1 for the galley sink, 1 for the shower, and 1 for the vent.

I'm struggling to figure out what fittings may work best for mating onto a flush ABS surface. Ideally I want them as flush as possible, and inside threaded - that way I can adapt whatever fittings I need externally beyond that point without having to disturb the tank side. Something that can either be threaded in from behind (Although that could be difficult, but not insurmountable) or fused using ABS glue would be preferable - it MUST be waterproof when it's all said and done as the tank is flush fitting against the floor of the trailer underneath - any water leakage will contribute to rot as it gets trapped between the tank and the floor. The fresh tank is also bigger than the sum of the toilet and grey so when it's full....I want it to come out the overboard dump/vent, not seep anywhere else and rot out my floor.

Anyone have any suggestions?

I can only think of two types of almost flush fittings. The standard plumbing bulkhead fitting which requires backside access to install and the Uniseal grommet type. I have used Uniseal in different sizes for many tank fittings. They are excellent.


https://www.aussieglobe.com/34-Uniseal- ... F8QAvD_BwE

that link is just for reference, not necessarily a recommended seller

First, not something I have done.

A quick examination of a few vendors for black and grey water plastic tanks. All tanks are delivered with a drain ( 1 1/2" to 3") and NO inlets. Inlets are custom added later. Water tanks on the other hand have several (typically 4) fitting built into the tank construction which are sealed. You cut out inner seal on the ones you use. The fitting are NOT flush. In addition, waste tanks (and water tanks) need a vent. Another fitting -- off or near the top surface of the tank.

Waste water tank inlets appear to always have some part that sticks up over the top surface of the tank. They generally consist of a grommet and coupler. These reasonably water tight. A typical vendor's products: (https://www.recpro.com/universal-rv-hol ... tings-kit/)

Inspection ports are about the closest thing to a flush fitting. They are not flush. And they have no mechanism to receive a fitting.

Your requested solution would entail a custom fabrication of an internal fitting which would be fused to a cutout on your tank.


Most likely the typical solution is to drill a bigger hole in the floor, having the raised fitting in the middle and the tank against the floor. One still has to make the connections to the other plumbing parts.

Thanks all - after a few false starts I ended up taking the tank to a plastic welder who not only made short work of patching up the gong show from the previous owner, but plastic welded on two inspection port bungs that work perfect for threading in some 1.5" barbed connectors to get the sink and vent plumbed into.