Holding tank fittings

[Brian]

We are installing a new polyethylene holding tank in our little Albin cruiser, but have run into a snag and hoping for some help from some of you.

The tank has "spin fittings" that are bonded in. The "in & out's" are 1 1/2" and the vent is 3/4" and are standard tapered pipe thread. The fittings I have bought are Marelon male pipe thread to hose
adaptors...http://www.forespar.com/products/boat-m ... lbow.shtml
Being "pipe thread", I thought these fittings would be tapered as well, and work with the tank inserts but they're not. I have tried them in the tank with teflon tape but they keep threading into the tank and don't tighten like I thought they would.
I guess these are not the correct fittings to use?
What type do I need?
Help!

Thanks

Brian

[RobS]

I believe this is what I used http://www.jamestowndistributors.com/us ... dapter+Kit

[DougSea]

Brian,

Looking at your link it seems your fittings may be NPS thread. I did a quick google search for "plastic NPT to barbed" and came up with a good number of hits. Stop off at your local plumbing supply or sprinkler company and you can probably find what you need. If you can bring the tank along, even better.

Let us know how it goes!

[Brian]

Thanks RobS & DougSea,

Ah, that makes sense, NPS/NPT.
I just called a plumbing supply and they say they can help me out. We'll see tomorrow!
I'm not a plumber, but I knew about tapered pipe thread.
So when someone says NPT it could mean NPS or NPT?
So where do you use the Marelon NPS fittings I bought?

[DougSea]

Thanks RobS & DougSea,

Ah, that makes sense, NPS/NPT.
I just called a plumbing supply and they say they can help me out. We'll see tomorrow!
I'm not a plumber, but I knew about tapered pipe thread.
So when someone says NPT it could mean NPS or NPT?
So where do you use the Marelon NPS fittings I bought?

NPS is straight, NPT is tapered. So in my comment I was referring to your Marlon fittings, which won't fit well with your NPT tank fittings. So...if the tank fittings are NPT your hose fittings should also be NPT. This is why plumbers get paid so well! They are versed in the black magic of pipe thread!