When we started using the upstairs toilet, the up and down toilets will not flush correctly. They flush sometimes when we hold down the handle. I have made the recommended adjustments in the tank, cleaned the holes around the rim, and the siphon hole. When I pour a bucket of water in the bowl, it will drain. I have coverde up the siphon hole with my thumb(cleqn water) and the bowl will drain during the flush. The toilets just swirl as the water rises and will drain back the their levels. Does this indicate that the vent has a blockage?