Help - Fitting T6 Under Chassis Waste Water Tank

[t0mb0]

Has anyone ever fitted one of these waste water tanks that fit in front of the spare wheel?

VW T5 T6 WASTE WATER TANK FITTING KIT MOTORHOME CONVERSION

I've just fitted one, and hooked it up but the drainage rate out of the sink is extremely slow. The drainage was fine before I hooked the tank up and I don't think I've squished or kinked the hose in.

I don't understand how they are meant to work because they don't appear to have any obvious way of getting air into the tank. If this is the case it could just be airlocked which would explain the very slow flow. However, if this was the case, then surely they would have fixed this obvious issue by now?

 

[stuart-t6]

Is there any form of trap between the sink and the new tank ? As I would be concerned about smell coming back into the van from the waste water tank.
I just let my sink drain outside but I am careful not to let any solids through leaving a mess behind when I leave site

 

[t0mb0]

Is there any form of trap between the sink and the new tank ? As I would be concerned about smell coming back into the van from the waste water tank.
I just let my sink drain outside but I am careful not to let any solids through leaving a mess behind when I leave site

No dedicated trap but the drain hose path creates a natural u-bend so this should be ok. We thought a tank would be useful so we can do things like brush our teeth in the van without worrying whether we've remember to stick a bucket under the waste water outlet.

If I can't make it drain properly though, I'll just have to give up and disconnect it. I'm tempted just to drill a hole near the top of the tank to test the airlock theory.

 

[rod_vw]

Does the sink drain quicker if you open the tank drain tap? If so then the tank needs a breather fitting in the top of the tank. I use small electrical cable glands with a short length of hard plastic tube inserted to vent and overflow when necessary. The glands are something like this IP68 WHITE CABLE GLAND NYLON WITH NUT PG7 PG9 PG11 PG13.5 PG16 PG19 PG21 PG29 | eBay

It does have to be fitted where you can reach inside the tank to fit the securing nut.

Rod

 

[t0mb0]

Does the sink drain quicker if you open the tank drain tap? If so then the tank needs a breather fitting in the top of the tank. I use small electrical cable glands with a short length of hard plastic tube inserted to vent and overflow when necessary. The glands are something like this IP68 WHITE CABLE GLAND NYLON WITH NUT PG7 PG9 PG11 PG13.5 PG16 PG19 PG21 PG29 | eBay

It does have to be fitted where you can reach inside the tank to fit the securing nut.

Rod

Thanks for the pointers!

It did definitely initially drain a bit quicker when I opened the drain tap, but still pretty low flow. However, with a sink full of water, it's now stopped draining entirely, even with the drain tap open. Could it be airlocked even with the drain tap open?

I didn't look very closely at the tank top before I put it on unfortunately but it looked like it had a couple of very small breathers, however, given it's tight up against the bottom of the van, these might be impeded. I'm sure I could add some breathers of some sort but I'd have to take it off again which I'm trying to avoid as it was a right pig to get on!

 

[rod_vw]

I gather it's a CAK tank so yes I think they do fit breathers as standard. It sounds as if you have a high point in the drain pipe which is causing an airlock. Even VW managed to do that with the early California!
I use tanks from Autocraft at Staveley which are the same as Auto Sleepers use.

Rod

 

[HotandCold]

I have this tank fitted, but configured as a fresh water tank, it has 3 small vents in the high parts of the top face and these overflow when the tank is full. Maybe your vents have become blocked?

 

[t0mb0]

I gather it's a CAK tank so yes I think they do fit breathers as standard. It sounds as if you have a high point in the drain pipe which is causing an airlock. Even VW managed to do that with the early California!
I use tanks from Autocraft at Staveley which are the same as Auto Sleepers use.

Rod

By ‘drain pipe’, do you mean the pipe connecting the sink to the tank? If so, this might be the case - I’ll see if I have any high points that might cause an airlock.

 

[rod_vw]

By ‘drain pipe’, do you mean the pipe connecting the sink to the tank? If so, this might be the case - I’ll see if I have any high points that might cause an airlock.

Yes, the one from the sink to the waste tank. If it's like mine it's only about 15mm so a high point will trap air and block / restrict the flow.

If you can try forcing the flow with a watering can of water poured as quickly as possible down the sink drain, this may prove the point by forcing the airlock. It's only temporary but may prove the point.

 

[t0mb0]

Yes, the one from the sink to the waste tank. If it's like mine it's only about 15mm so a high point will trap air and block / restrict the flow.

If you can try forcing the flow with a watering can of water poured as quickly as possible down the sink drain, this may prove the point by forcing the airlock. It's only temporary but may prove the point.

I've tried forcing a large volume of water down and it doesn't seem to help.

I tried rejigging the pipe to try and avoid high points. Initially it seemed to work but then as I cable tied it, it stopped flowing again. It seems incredibly sensitive to the precise route of the cable and given it's got to go around chassis supports, exhaust, suspension etc, then it's a real pain to get right.

I've pretty much had enough of it, might give in and take the tank off - if it's that sensitive then presumably having the van on a slight slope etc could affect it.

 

[rod_vw]

Why not take the pipe off the tank end and tie it up as near as possible to that location and see how the water flows? If it's the same then you have proved the problem is not the tank.

I've still not perfected mine and I expect that it's a shorter run than yours as the sink is behind the driver's seat and my waste tank is a centre chassis mounted one with the input at the back. I've done four T5/T6 conversions and all have had a slow sink drain. The waste pipe runs down behind the fridge, into the hollow chassis/body side member, exits that a bit further back and loops below the exhaust and up to the waste tank. The problem is certainly airlock in the pipe as slight differences in angle of the van affect the flow rate. Strangely the leveller the van is the slower the sink drains, but it's bearable.