We have a common problem with missing drain bungs and it can be quite hard to find replacements sometimes, these ones are fairly shallow underneath so we have been able to screw over top of moulded in thread holes or cut out and then screw down flat. so you have 2 screw holes in each bung and I normally use small stainless steel self tappers and whack a bit of silicon around the hole for a better seal if I am feeling keen
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