... In my pool at home, with my weight belt on I have tried on my knees in the shallow end. I am able to put my head in the pool with the snorkel in my mouth and no mask but when I try it a foot down is when I have the problem (pressure?). I have tried without the mask, holding my nose and then letting go and same thing - sinus irrigation! ...
Questions, Are you comfortable swimming in your pool without a mask or nose clip?
Can you dive to the bottom of your pool in confidence as well?
Do you feel the mask pressing against your face as you descend?
If you are comfortable in the pool without a mask and you feel mask pressure as you descend then Id suggest learning to equalize the mask as you descend (very slight puff from your nose). Then, before removing your mask under water, puff a little air from your nose as you remove the mask. It only takes a slight amount of air pressure from your nose to prevent water from entering it. After some practice, this practice will become second nature.