I have used and still use teflon tape and never had an issue.I won't silicone the bulkhead threads, but the threads of any other threaded connections in the plumbing where water goes through the connection will be. People recommend teflon all the time but from what I've seen, it is not meant for PVC. It's meant for metal fittings. Silicone is an easy aquarium safe alternative sealant choice for the threads.