If you have not opened an engine-block welch plug during
your fluid draining procedure , then don't do so . The fluid in the
radiator , two rubber pipes and the coolant expansion bottle
is enough volume . These are very small systems and could
economically be done every year really.
If a welch plug has been opened , then removing the thermostat
and flushing water through the plug hole with a hosepipe , until
there's no bubbles ,is the only sure way I know of removing air.
Hold the thermostate housing with one hand and the hose with
your other , so that your ready to press it down ( air-tight then)
the moment your happy , and whilst the hose is still running.
NO fluid will then be lost from the plug hole if air can't get in
the top.