Sta-Rite Filter/New Sand and Prime Issue

My filter is an old Sta-Rite. The base's feet over the years had been cracking/falling apart one by one. I had chlorinator removed years ago (made obnoxious noise even without pucks in it) when I adopted the BBB method.

In AL, I simply plug one skimmer hole (no floor drain), return jets and drain the filter, pump basket and moto each fall. Before I opened a week ago I unwinterized everything to start her up and check CL level; I have always opened to crystal clear water and this was no exception.

But because the filter was leaning so much due to the broken feet on base I had several pvc leaks on intake and discharge lines. My pool liner/repair guy never returned my call. 60 and not a handy gal, a guy friend said he would fix it at a nominal cost. 13 yrs of my ownership the sand had never been replaced so decided good opportunity.

In ground, 20k gal, Sta-Rite, 1/2 hp Hayward pump replaced a season ago.

We ordered a new base. Unfortunately eons ago someone glued the base to the bottom of filter so we scraped off with heat gun. He leveled it perfectly with leveler. Looked up directions for my older type of Sta-Rite and added first water then added 300 lbs of #20 Silica sand from pool store and added after putting water in first, making sure that center baffle pipe was perfectly centered; he even measured it to make sure. He glued that white plastic moon looking thing to the multiport and locked it down; the o-ring looked pliable and perfect. On the two butchered intake and discharge pipes he added two couplings on each line with o-rings. I have a ball cock valve on the waste hose because years ago it would leak a little. Very old but simple system. Multiport was replaced when liner was about 6 years ago. Works fine.

So here's the problem. It won't get 100% prime. Plenty of prime for pump and vacuuming--same good suctioning ss ever. But there are air bubbles in top of pump basket when there shouldn't be, air bubbles coming out of shallow end of jet, which there should be, and an obnoxious chortling sound coming from valve head/multiport. He has taken it apart sever times and sees no problems. Following procedural directions I backwashed and rinsed a couple times. Lost a small amount of sand which was expected was expelled but just thru waste hose, not any in pool.

All this screams air leak to me but again, with first really plumb intake and discharge pcv pipes and absolutely no leaks anywhere, what could the problem be?

Fyi I learned the BBB method on this forum a long time ago, perhaps 11 or 12.

Would really appreciate any help. Liner/repair guy still isn't returning my call. And on disability now really don't need the xtra expense of housecall. Got very good deal with guy friend, not pool guy but brilliant when it comes to almost anything. All I can think of is maybe one of the o-rings on one of the new four couplings isn't seated right but again, not one water leak anywhere. The o-ring on pump basket appears to be well seated too, and should've been replaced with new pump a season ago.

Thanks so much for any ideas. The constant water chortling noise coming from valve head is quite annoying. He even opened up and lowered water a little, remembering that it was a little higher than when he first opened it up.

Thanks again,
Elsie