I'm a plumber and I would suggest staying with the slip fitting threaded seems to always find a waY to leak on my reflow pump I had to connect a 1.5 threaded fitting I used Teflon and then reef safe silicon year and a bit later it found a way to slowly leek. As hllywd said use unions if wanna cut and put back together. And by the way sch 80 is crazy over kill on a reef tank sch40 is just fine. In canada we use sch80 for higher pressure lines in the dirt. Example water distribution under a large warehouse.
Well, it is not surprising that you are having/have had problems with keeping the joins with your reeflo pump from leaking. The instructions, supplied with every pump Reeflo sells, clearly state to use a non-hardening thread sealant NOT teflon tape. Using silicone obviously does not help one bit, and silicone + pvc is a really bad combination.
The PVC fitting manufacturers (Lasco and Spears in particular) say that tape is the wrong way to seal PVC threaded joins, and that a non-hardening thread sealant should be used, as even a single wrap of tape, starts to deform the threads/fitting becasue the threads are tapered; tape lubricates the threads encouraging overtightening which further distorts the threads/fitting. They also say that a thread sealant, that does not contain teflon, should be used, as with plastic fittings a lubricant is not needed nor desirable.
Tape is for metal threaded fittings to prevent galling. Plumbers that actually get this right are the exception, not the rule.
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As to the general discussion in this thread, in just about every case, only two threaded joins are required in an aquarium system and those are both at the pump: the inlet and the outlet. (just the outlet for submersible.)
Although threaded fittings are way overused in the aquarium hobby, sometimes you have to use them (case by case basis, at the pump for instance.) Use a non-hardening thread sealant, and follow the directions (e.g. read them) By applying the sealant per directions, the odds of a leak developing are very slim.
Union use in aqaurium systems is also abused. Again, there are only two unions required: both at the pump. Much of the time, unions are not installed properly and are overtightened, which causes leaks. Overtightening damages the o-rings. Union o-rings should be lubricated to prevent damage using a silicone
lubricant. Hobby wise, the only supplier that markets this product is Lifegard Aquatics, part number: R172036X. Nothing should be applied to the union body threads, the o-ring seals the union, not the body threads. Hand tight is enough, tools should not be used.
That leaves solvent weld joins. Folks are lulled into something of a false sense of security, that being solvent welds won't leak. That just isn't true, and the "leaks" can be more insidious and difficult to find. Often a leak in a solvent weld will not show water, but will suck air in creating micro bubbles in the return plumbing, and preventing siphon drains from working properly.
The directons on the cans of glue are pretty clear, but many do not read them. (Incidentally, the directions state: use primer
IF required. This is alluding to building codes. It is also makes it pretty clear that primer is
NOT required for good solid solvent weld joins, unless the pipe is "dirty", i.e. been buried in the ground.) Poor gluing technique is responsible for leaks in solvent weld joins, (folks seem to think primer will take care of this, it won't.)
I don't think it matters what type of joins you have in your system, because leaks are caused by not following the directions, not an inherent flaw in a particular joint type.
Sch 80 is a real waste in this hobby. However, Sch 80 unions and valves (with viton seals) hold up better, than sch 40 valves and unions. (I use sch 40 spa fittings for connecting pumps, but just the same.) But with sch 80 valves and unions, there should not be a threaded connection to the rest as both Lasco, and Spears recommend agains mixing sch 40 and sch 80 theaded fittings.
