the curved surfaced never mattered to me because im not trying to seal metal or hard plastic buckets. If you tighten it down it flattens the plastic and creates a seal. Its only a 2 inch hole so it doesnt have any trouble pulling a rubbermaid or 5 gallon bucket plastic flat. that shit is thin and flexible plastic.
I use a brass hole cutter and I have an edge scraping deburring tool as well. My holes are smooth as my wifes hairless ass.
sorry, cheetos, but i call b.s.
I've tried bulkheads on 5-gallon buckets from hydrofarm, home depot, and lowes. you might be able to flatten the bucket somewhat, but you'll never get a seal with a bulkhead, especially at the bottom of the wall where the bottom of the bucket will prevent you from flattening the bucket (and where you usually want the drain). even the top of wall will be tough with the lid locked in place.
in order to get THAT much pressure to flatten the bucket to the point where the grommet will be compressed and for a seal, the torque is likely to strip the nut or threads of the cheap plastic bulkhead or break the flange before you ever get it to stop dripping. i know because i've had all three of these things happen.
better yet, try that in a 20-, 32-, or 55-gallon rubbermaid "brute" garbage can, again, near the bottom. with 2-3ft of water head, your garbage can will have completely drained itself through the leak with a bulkhead within an hour, if not minutes.
again, these aren't grommets for barbs and vinyl tubing. uniseals are designed for used with rigid pipe.
here's one of the 20-gallon garbage cans that tops off my flood/drain res. that's 1/2" sched40 PVC, btw. notice the can is almost full of water and there isn't any sign of leaking on the can or floor. no way in hell you can pull that off with a bulkhead.
another bonus: the pipe slides through the seal uncut. here are pics of a 3/4" drain on a flood tray. it's a flat surface that i could've used a bulkhead on, but with a uniseal i can adjust the water level by just sliding the 3/4" PVC up and down through the seal with a little plumber's silicone lube. with a bulkhead, water level is fixed or requires a bit more complexity to adjust.
here's an extreme example of what you can do with them, pulled off the web. the tighter the radius, the more impossible it's going to be to seal with a bulkhead. again, no way in hell this would be possible with bulkheads. just goes to illustrate that bulkheads are not designed for nor will they seal ANY curved surface, regardless of how tight the radius is. uniseals do work on ANY curved surface and they also work just as well on flat surfaces.
uniseals' low profile is also a bonus. the male threaded part of the bulkhead that you screw the nut onto is going to stick out, either on the inside or outside. for smaller pipe diameter, it isn't a big issue, but a 1-1/2" bulkhead does require about 2-1/2" of clearance. the 1/2", 3/4", and 1-1/2" bulkheads are all about 1/2" thick.
i doubt i'll convince cheetos, but anyone else wondering how to seal a hole in the side of a bucket, here you go. a bunch of reasons to use uniseals.