The instruction manual of some 1-18 washers with a pre-wash option said you could use the fabric softener dispenser as a liquid detergent dispenser for the main wash. Otherwise the only dispensers available were the bleach dispenser and the fabric softener dispenser. The centre of the jetcone could be used as a powder detergent dispenser if you pour the powder below the bleach dispenser or if you don't use the bleach dispenser. I never cared doing that but I did use the fabric softener dispenser to dispense liquid detergent when I used the pre-wash option.
See pages 3 of the manual in the link below for how to use the agitator itself (not the bleach/dye dispenser that fits inside!) as a powdered detergent dispenser and how to use the fabric softener dispenser to dispense fabric softener.
See the page 4 for how to use the fabric softener dispenser as a liquid detergent dispenser on washers with the pre-wash option (that won't work on models without the pre-wash cycle).