Use the device argument 'rtl_tcp=192.168.0.108:1234' in OsmoSDR (gr-osmosdr) source
to receive samples in GRC and control rtl_tcp parameters (frequency, gain, ...).

[comment: here I click on "play" in SDR#,. then these lines show up:]

client accepted!
set gain mode 1
set sample rate 2048000
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
set freq 100000000
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
rtlsdr_demod_write_reg failed with -4
rtlsdr_demod_read_reg failed with -4
set freq correction 0
worker cond timeout
Signal caught, exiting!
comm recv bye
Signal caught, exiting!