I'm replacing the livewell pump in my boat and was wondering what type of sealant to use on the thru-hull fitting. The hull is aluminum and the pump tube and fitting are plastic. I was checking out 3M 5200 but it didn't specify whether it would adhere to metal. Just wondering what some of you have used. Thanks

Do not use 3M 5200 on anything that may need to be removed or replaced down the road. Use a marine grade silicone sealant. Put a quarter inch bead of silicone in the corner of the threaded tube and the outside flange.

Install the fitting and squeeze the silicone slightly so it spreads. Do not tighten the fitting until the silicone sets up. Once it sets up, you have a silicone washer/gasket that will not squeeze out. It will compress, forming a perfect seal.

I learned this trick when installing new windows on the wheelhouse of my lobsterboat. If you tighten it down while it is still soft, there will be no thickness of silicone left to compress.

I'm a great advocate of 3M 5200, but not for your project.

Thanks Rhino, I didn't realize 5200 was permanent. It would have been a real pain the next time.

Thanks Rhino, I didn't realize 5200 was permanent. It would have been a real pain the next time.

5200 very clearly states on it that it is permanent. It will not come off. Never put that on anything that you have any inkling of removing in the future. It's some strong goop.

If you do what Rhino said, you'll be good to go. Silicone is some great stuff if it's used properly. Just make sure you let it fully cure before you tighten down on it all the way and you won't have a problem.