Hi,
You can type this to a gr-osmosdr block in GNU Radio. I doubt that GNU Radio would be easy to compile on Android.
If you want to write your own client that processes I/Q data, you should look at
rtl_tcp source code, it's quite self-documenting.
Anyway, some key points: if you open a TCP connection to the rtl_tcp server, it immediately starts to send you the 8-bit I/Q samples acquired from the dongle. Every odd byte is an I, every even byte is a Q sample.
You can control rtl_tcp with five byte commands. Look for "switch(cmd.cmd)" and "struct command" in the source code.
When your client connects, it also gets 12 bytes with the dongle identifier at the beginning of the stream, but it can be ignored. Look for "dongle_info_t" if interested.
You will need to process the I/Q data yourself and calculate FFT to draw the waterfall.
Regards,
Andras, HA7ILM