Good morning Peggie,I have had a three to four month on going battle with the head in my cat 30. Its a wilcox original 1981 issue, I beleive. So far there is no winner in this battle!!!!The senerio is as follows:develooed back presure when pumping, had holdong tank pumped out, still back presure. Followed your advice in other posting and reran the vent from the original 5' snake to a short straight up line. In doning so pulled line off the holding tank and discovered, the hard way, that the tank never pumped out (clogged vent i suspect). Any way, repumped the tank and all was fine til the weekend.Now I have developed a new problem....When i flush the head and place the pump in dry mode the head fills up with what i beleive to be raw water within 30 minutes, punp it out and it fills back up. It will fill to the top of the rim and that is as far as it goes (so far!!). I have closed the raw water thru hull to the head and am monitoring the water level, but am looking for some guidence as to my next attack. Where do aI go from here???Thanks Peggie for your time spent, I've made it this far only because of you imformative postings bobcat