Waste Tank Inlet Pipes Too Long in 2008 Apache?

[DaveFromBarrow]

As I continue to "debug" my MH (2008 Apache 634) I want to solve this issue.

Waste tank empty - all plugs drain well.
Waste tank has two or three buckets full of water - plugs drain slowly. Opening the waste valve = plugs drain down normally.

My thinking is the waste pipes are too long and sit in the bottom of the waste tank and once there's a small pressure of water in the tank there's not enough pressure in the pipes to overcome this resulting in poor drainage.

My solution, unless advised otherwise, is to shorten the waste pipes so they only go into the waste tank by 50-75mm.

Anyone else had this issue?

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[Landy Andy]

I don‘t have this issue but could be that the tank is sealed so as you try to add water to the tank it has to push air out the tank to allow room for the entering water?

Blocked, or no air vent to tank?

 

[DaveFromBarrow]

Thanks Andy. However, I had the tank removed by the local garage earlier this year so I could inspect it and replace the level sensor. The waste pipes enter via generous holes in the top so I'm pretty sure it's not sealing - but I'll check. I meant to check the waste pipe lengths when they did this but got sidetracked.

Apart from needing to work under the vehicle, it's not a big job to drop the tank so I'll do that and test my theory. I was just interested to hear if anyone else had come across this.

I think my reasoning is sound but then again, it's a motorhome.....

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[Diabalo]

The head of water in the sinks should in normal circumstances overide any pressure due to the pipes being too long, I would be looking to see if the vent is blocked

 

[DaveFromBarrow]

The tank's open to the atmosphere by virtue of the waste pipe entry points - from memory. But I'll certainly check that and perhaps add a dedicated vent if there isn't one. Autotrail didn't bother to pack the window frames so it wouldn't surprise me if they forgot to add a dedicated vent

I think if the pipes went directly down into the tank the likelihood of the tank water level creating enough pressure to stop the pipes flowing would be slim, but given they don't, it might I guess.

I know from research flow rates can be hit or miss - vehicle levelling being an obvious cause of poor drainage, but on level ground sinks should just drain at a reasonable rate I would have thought.

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[Landy Andy]

If the pipes are long, and you have no vent then filling the tank would increase the pressure in the tank trying to force water up the pipe?
Again just thoughts. Have you ever overfilled the tank to see if it has a vent, or overflow?

 

[Diabalo]

The tank is not open to the atmosphere unless it is vented, as all of the sinks should have traps, if they didn't have traps the smell from the tank would be coming up the pipe.

 

[DaveFromBarrow]

Ah OK, what I'm saying is the holes the pipes go through to enter the tank are not sealed - to the best of my knowledge. This means the tank is open to the atmosphere.

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[DaveFromBarrow]

So here's the tank removed. As you can see, it's got three holes for the inlets and two spares, in the corners, which I guess are vents. So it can't be suffering from a lack of ventilation.

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[Landy Andy]

Ohhh. Ok. I thought you would have spigots on the tank, that the pipes then connect to. As you say, it looks like there is plenty of free air.

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[Itsmcb]

That's a very poor design. If your tank is full does the (smelly) water not just splash out through the holes as you drive off your pitch or along the road? Ideal if your on grass and can't be bothered to empty it I suppose although the smell must still waft out in hot weather.