Bulkhead fittings to PVC

[landscraper]

Hi Everyone... I am trying to get my pre dilled 90 gal bulkhead fittings to convert under the tank to hard piped pvc... I have a 1" Drain bulkead with threads on the outside of the bulkhead and a slip inside, and a 3/4" return bulkhead with threads on the outside and inside. I really want to use the outside threads on the return so I dont decrease the flow.... Problem is None of the PVC pieces thread onto either of these.... Am I missing something??

 

[al&burke]

The outside threads on a bulkhead are straight threads - the inside ones are NPT - which are pipe threads - they are tapered so that as you tighten the fittings they make a perfect seal (with teflon tape or pipe dope) - I have never connected anything to the outside threads - you have to work with the inside of the bulkhead, being a NPT fitting or slip fitting. Maybe someone else on here knows different, let's see if they chime in.

 

[landscraper]

Thanks.. Yea it just seems strange.. I mean if there are threads.. besides the nut that holds them on I would think there would be a way to thread a PVC elbow or something on

 

[al&burke]

The bulkhead thread serves a different purpose, to make a perfect conection to the tank.

 

[spanko]

The outer threads of a bulkhead are not for plumbing fittings. No PVC parts will screw onto that section, but some conduit fittings sold in the electrical section may fit. Don't use the outer threads for plumbing; they are there for the retaining nut to tighten the bulkhead in place. A slip fitting glued here is the preference.

 

[landscraper]

Thanks guys.. makes sense the more I look at it.. I just didnt want to restrict as much flow as I could.. .but oh well..
Thanks!