In-ground suction leak

I had trouble priming my pump. After verifying that the pool level was sufficient for the skimmers and the replacement of the pump strainer o-ring, I was able to start the pump by isolating water to the pump with only the main drain and vacuum lines as input. The pump now runs without any bubbles when the skimmer feed valve is turned off; the valve is positioned just prior to the pump.

Between the skimmers (2) and the pump is a Pentair check valve; my pump is 4' above grade. I've applied fresh silicone to the check valve cover to no avail.

So, I'm looking for recommendations to determine how to troubleshoot the suction leak on the skimmer side input to the pump. So, is there any way to leverage the fact that there is a check valve between the pump and skimmers and if so, how?

The presence of the check valve suggests that someone had (or expected) priming problems before. As a first step, I'd recommend the following:

1. Get the running normally on the main drain and vacuum lines.
2. Turn the pump off and *quickly* close the main drain and vac line valves. (Hopefully, these valves don't leak.)
3. Open the skimmer line, and open the pump strainer basket lid.
4. Use a hose or bucket to fill the pump basket.
5. If the check valve is working, you will be able to fill the basket, and the skimmer line up to the skimmer. If you cannot do so, replace the check valve. (Depending on the valve, the easiest way may be to buy a new identical valve, and swap out the new valve guts for the old.)
6. Once the check valve is working, and the skimmer line is full, close the skimmer line valve and the pump basket and restart the pump.
7. Once the pump is running fully, open the skimmer valve slightly, until bubbles appear.
8. Close the valve, and leave it closed till the pump is again running normally.
9. Repeat, up to 6x.
10. If the skimmer line every runs bubble free, open the skimmer valve completely, and you should be good to go.
11. If the skimmer line never runs bubble free OR if bubbles gradually build up over the next hour of pump operation, you probably have a suction leak (letting air IN) somewhere in the piping between the skimmer and the pump.

Thanks for the quick response.

Just so I'm not missing anything, on step 6 I should reopen the main drain and vacuum lines prior to restarting the pump, right? Otherwise, all the directions are very clear. Again, thanks!

sorry, I overlooked this.

Yes, that's what I meant.