i would just say no as a gut reaction. Brass is copper and zinc. you're working so hard to clean the water why would you risk it? Even brass slowly oxidizes over time and that means something nasty (copper ions I think) is going into the water that you are wasting 10g/g to make. Home depot and menards both carry mur-lock push fittings and bulkreefsupply will have it here tuesday if you order it monday. Which fitting is it? Show us a picture. Maybe another reefer has that one. Granted, There are some people using tap water and if the brass is upstream of the RO/DI then you'd remove whatever you adding from it I guess, so I may be contradicted here, but remember that when the RO/DI is off it's still full of water and that brass will just be soaking in it. For me personally I would not risk it.