I have noticed on occasion my holding vent sometimes spits "water" when the head is being pumped. Yuk! The holding tank does not appear to be full either. Wondering, what might be causing that? Thanks...
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Several ifs. If the vent line is small in diameter
and if there is a low place in the line and if there has been some sloshing then you could have water in the line and pumping forces material into the tank and air out the vent. The water gets push out too. Inspect the vent line for a constant slope that will drain back into the tank. Consider installing a short larger diameter section of pipe in the vertical section of the vent thereby creating a "Wide place in the road" that will allow the air to bubble through the liquid and not blow it out.
and if there is a low place in the line and if there has been some sloshing then you could have water in the line and pumping forces material into the tank and air out the vent. The water gets push out too. Inspect the vent line for a constant slope that will drain back into the tank. Consider installing a short larger diameter section of pipe in the vertical section of the vent thereby creating a "Wide place in the road" that will allow the air to bubble through the liquid and not blow it out.
Ross has it almost right...
Even a half full tank can spill into the vent line when the boat is heeled if the vent fitting is outboard on the tank...doesn't matter what the diameter of vent line is. If there's a sag in the vent line, waste will be left sitting in it. But a "wide spot in the road" that will allow air to bubble through any waste sitting in the line is not the answer, 'cuz waste allowed to sit in the vent line will eventually block it. Even if it doesn't sit in the line, it'll still build up and block the vent at the tank and at the vent thru-hull. So the solution to the problem is: straighten out the vent line...and to make sure the vent doesn't ever become blocked, backflush it every time the tank is pumped out and/or you wash the boat. If the vent thru-hull isn't a design that will allow you to do that, replace it with a thru-hull that will.
Even a half full tank can spill into the vent line when the boat is heeled if the vent fitting is outboard on the tank...doesn't matter what the diameter of vent line is. If there's a sag in the vent line, waste will be left sitting in it. But a "wide spot in the road" that will allow air to bubble through any waste sitting in the line is not the answer, 'cuz waste allowed to sit in the vent line will eventually block it. Even if it doesn't sit in the line, it'll still build up and block the vent at the tank and at the vent thru-hull. So the solution to the problem is: straighten out the vent line...and to make sure the vent doesn't ever become blocked, backflush it every time the tank is pumped out and/or you wash the boat. If the vent thru-hull isn't a design that will allow you to do that, replace it with a thru-hull that will.
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