Answer is: in through the pores and out through the osculum.
Water enters the spongocoel (central cavity of sponges) through tiny pores and exits through the osculum (excretory structure).
The spongocoel is filled with choanocytes (collar cells), which have flagella that push water through the spongocoel, creating a current.
Sponges pump large volumes of water, approximately a volume of water equal to the sponge's body size is pumped every five seconds.
Sponges are the members of the phylum Porifera.
