The ink absorber box or flushing box needs to be replaced. 
> Contact Brother customer service from the "Contact Us" section.

These components may require periodic replacement to ensure optimum performance from your Brother machine. The replacement cycle depends on the number of purges and flushes required to clean the ink system. The more cleaning the machine requires, the faster these boxes will fill up. The use of non-Brother ink may cause frequent cleanings because non-Brother ink could cause poor print quality, which can be improved by cleaning.

The machine automatically cleans itself:

1. If you have removed the power cord and plugged it back in.
2. If you have cleared a paper jam.
3. If you have not used the machine for more than 30 days.
4. If you have replaced ink cartridges of the same color 12 times.