Hello: I believe the element threads are 1-1/4″, so you’ll need to bush down to 3/4″. I’ve watched these tanks since they came out and not heard of any significant problems other than some hoop jumping to get warranty in one case. (don’t ever let them dry fire!)
Here is a study that discusses how plastics leach into water and also how they allow things outside the pipe to permeate through into the water. http://water.epa.gov/lawsregs/rulesregs/sdwa/tcr/upload/permeationandleaching.pdf
You should read it, but to summarize, permeation is a problem where there is something to move across the piping and leaching doesn’t seem to be a problem with polybutylene, (unlike PVC).
The bad rap was largely fitting failure rather than pipe failure. The pipe did have problems in over-chlorinated water.