You note you've got a West Marine (WM) nearby and Kevin said he used Defenders. I just did a bunch of replacements - WM was $7.29 for the Scandvik ABA 316 SS SAE10. A local FL store (Boat Owners Warehouse) has it for 3.92 and Defender is $2.99. Buying many clamps makes Defender's shipping charge minor. Scandvik ABA is excellent. WM has Scandvik add a digit to the clamp number so they can call it a private brand and refuse to price match, saying it is not identical - it is.
Double clamping has been highly recommended for thru-hulls (with long barbs). Not important for fresh water, sea water on pump discharges and engine coolant as you likely won't sink if those go.
My project was the hot water tank. To clean just remove all the hoses and electric feed, then drain and take it out of the engine room. Pull the heating element and plumbing fittings. Then rinse thoroughly, shaking it around and upside down to slosh out any sludge. If you've got rusty sludge, rinse and slosh some more with a bunch of phosphoric acid to passivate. Reassemble with fresh teflon tape on the pipe threads and maybe put in a new heating element - every few years is good for those - and do check the wiring for any electric corrosion. Don't forget the clamps on the copper distribution pipes along the hull - mine were buried in sound insulation and rusting badly.
Mine is a 16 year old IsoTemp that had a tiny leak at the hot outlet that dripped down and corroded the thermostats. I had patched a side wall leak with JB Weld 15 years ago and that was still good (JB Weld rocks!) but I peeled that off anyway and redid both with a new JB Weld "Marine" version for $8. Replacement generic button thermostats = $3. Replacement heating element $12. Total repair $23 vs new IsoTemp at about $700. I did put it on the "repair-again" list for 2035.
Craig - SN68 Sangaris, Tropic Isle Harbor, FL