if its engine exhaust it should have nothing to do with the blower or the waste tank having water in it.
you probably have a internal leak inside the heat exchanger that is on the engine exhaust.
If you can isolate pressure on the heat exchanger with a pressure gauge on it once the pump shows pressure you can shut off a ball valve on the inlet and the outlet of the heat exchanger and it should hold pressure on the gauge. If the pressure leaks down then you fo sho have a leak inside the heat exchanger.
You could also plug one of the inlet/outlet fittings and rigg up a connection to hook up to a air compressor on the other. again it should hold pressure. If you do it without the engine running you should be able hear the air if it is leaking internally.