i have used waxoil. Best thing to do is thin it down by maybe 1/3 or 1/2 then slow put it the frame and leave the frame at loads of angles and move it around lots for some time. Then leave to cure. Best done on a dry day and ideally warm environment. Best to clean the thread and leave it for few days to harden. Also do not put the bike near a radiator for some time after! Had some come out a little for a week or two,after. But never had a problem since, even in very hot weather. Bit of aggro but worth it imo. Do not put too in esp in, neat and thick as most of it will stay in the frame and could add a fair bit of weight if that matters. Also I recon putting it in neat is not good as it’s unlikely to get into all the little nook and crannies and just bung up bits internally.1/3 thinner or 1/2 thinner diluted with white spirits iirc seems best.
It will also make your bike smell for a few weeks, but this goes. It can take a few weeks to settle and cure properly.
Sound like hassle but not too bad. Also you can get spray cans of the stuff which is probably more costly but iirc thinner from the off. If using normal stuff put the can in hot water for a while thinning / applying.
Also put the seat tube in and out after it has cured a bit, rather than 2 weeks later.