how can I temporarily plug overflow holes

[Thizz]

doing a new build and want to completely rinse out my tank for a fresh start.

if I don't have any spare bulkheads on hand to cap off, what can i do to plug 3 holes in the overflow box? I've never tried it but would flex seal tape work or would the pressure make it release over a few days

 

[BeanAnimal]

simple slip or threaded (depending on bulkhead) pvc plugs will work.

 

[TangerineSpeedo]

I second some cheap bulkheads on amazon and pvc plugs.
You could get some fancy blow up things plumbers use to test systems, but bulkheads are probably cheaper

 

[carri10]

not sure where the pressure will be coming from, and therefore how much it needs to resist, but some rubber bungs work well for me when I want to temporarily close my overflow/return pipes.