How do you to a refill bc 31m ink cartridge?

Question

type of printer: brother: MFC 3820cn

Answer 1

your cartridge is LC800, refilling these cartridge can be a mess and don't work. You will be better of to purchase compatible ink cartridge for your printer. These cartridge is cheap.

Answer 2

I have never heard of anyone having luck refilling these cartridges.  In fact it's almost impossible to find refill kits for these particular ink cartridges.  I'd also suggest compatible ink cartridges instead which can only cost $3-5 on sites like http://www.castleink.com