PTFE plumber's thread sealing pipe dope (or something close to that) or you can use Teflon tape. The yellow tape is for gas fittings. 

Karl Wolz
Sent from my electronic umbilicus

> On Jun 5, 2014, at 6:36 PM, Mike South <msouth@GMAIL.COM> wrote:
> 
> So, I have a new replacement propane tank.  The only part I kept from the
> old tank is the "splitter" that leads from the tank to the two lines going
> in to the van (one fridge, one stove).
> 
> I'm wondering if there is some kid of thread compound or something I should
> use when screwing that on to the tank output.
> 
> My understanding is that on the flared fittings you do not use any compound
> (correct me if this is wrong).  But this isn't flared, it is just one block
> of metal screwed in to another block.
> 
> mike